The present invention relates to an ignition system for an internal combustion engine. More particularly, the invention relates to a distributorless ignition system suitable for an internal combustion engine such as, for example, an automobile engine.
For modem ignition systems associated with internal combustion engines, ways are constantly being sought for extending the useful life of such ignition systems and avoiding the premature necessity of repair and maintenance commonly associated therewith.
One particular way of extending the life of ignition systems has involved the development of an ignition system which does not incorporate a traditional distributor. Such a xe2x80x9cdistributorless ignition system,xe2x80x9d sometimes referred to as a xe2x80x9ccomputer-coil ignition system,xe2x80x9d typically includes, for example, spark plugs, one or more ignition coils, a coil control unit, a computer (such as an engine control module or ECM), and engine sensors. In this type of ignition system, each individual spark plug is functionally associated with an individual cylinder of the engine.
In such a distributorless ignition system, the coil control unit has an electronic circuit for electronically controlling and electrically driving the ignition coil(s). Each individual ignition coil has a primary winding and a secondary winding wrapped about a core. The ends of the primary winding are connected to the coil control unit, and the ends of the secondary winding are wired to two spark plugs. Each spark plug has a center electrode and an outer (or ground) electrode separated by a spark gap. In a xe2x80x9cwasted-sparkxe2x80x9d ignition coil configuration, for example, the center electrodes of the two spark plugs are simply connected to opposite ends of the secondary winding, and the outer electrodes of the two spark plugs are both simply connected to electrical ground. Thus, given that each individual spark plug is associated with an individual cylinder of an engine, a four-cylinder engine having such a distributorless ignition system generally has two ignition coils. A six-cylinder engine, therefore, has three ignition coils.
During operation of the distributorless ignition system, the engine sensors sense engine operating conditions and/or positioning information and pass corresponding data in the form of electrical signals to the engine control module. The engine control module generally interprets this engine data and sends electrical pulses to the coil control unit which dictate ignition timing. Some types of sensed information, however, such as crankshaft position data and/or camshaft position data, may instead be sent directly to the coil control unit without first being interpreted by the engine control module. Once the coil control unit receives ignition timing pulses from the engine control module, the coil control unit then controls and successively drives and applies electrical current through the primary winding of the ignition coil(s). Each time the applied electrical current in the primary winding of an ignition coil is turned off, the magnetic field that was built up in the core of the ignition coil during application then collapses. As a result of the collapse, a brief high-tension current is induced in the secondary winding of the ignition coil. This high-tension current is sufficient to cause simultaneous firing (that is, xe2x80x9carcingxe2x80x9d or xe2x80x9csparkingxe2x80x9d) across the individual spark gaps of the two spark plugs which are connected to the secondary winding of the ignition coil. In this way, the simultaneous firing of the two spark plugs is directly related to current engine positioning data and is therefore properly synchronized with the stroke cycle of an internal combustion engine.
A distributorless ignition system as described above has several possible advantages over other types of ignition systems, such as a distributor-based ignition system. These advantages may include one or more of the following: (1) no rotor or distributor cap to burn, crack, or fail; (2) utilization of computer-controlled spark advance ignition timing without the sticking and wearing of mechanical weights; (3) no vacuum advance diaphragm to rupture or leak; (4) any play in timing chain and distributor drive gear is eliminated as a problem that could upset ignition timing; (5) a crankshaft position sensor is not affected by timing chain slack or gear play; (6) there are fewer moving parts to wear and malfunction; and (7) less maintenance is required since ignition timing is typically not adjustable.
In many conventional distributorless ignition systems wherein each ignition coil fires two spark plugs simultaneously in a wasted-spark configuration, successive applications of electrical current are directed and driven in only one direction through the entire length of the primary winding of the ignition coil. Thus, each time the current in the primary winding is turned off, the magnetic field associated with the core of the ignition coil collapses, and the resulting current induced in the secondary winding of the ignition coil always flows in one particular direction. Given that the two spark plugs connected to opposite ends of the secondary winding are connected such that their outer electrodes are both connected to electrical ground, one plug is then always relegated to firing only with a positive polarity while the other plug is always relegated to firing with a negative polarity. See, for example, U.S. Pat. No. 4,216,755 issued to Ordines on Aug. 12, 1980.
Experience has demonstrated, however, that always firing one spark plug with a positive polarity on its center electrode (that is, positive firing) and always firing the other spark plug with a negative polarity on its center electrode (negative firing) is not desirable for purposes of extending the useful life and avoiding the premature necessity for repair and maintenance of an ignition system. In particular, the plug which fires with a positive polarity typically requires a higher firing voltage potential between its two electrodes to successfully xe2x80x9cbreak downxe2x80x9d the spark gap (that is, produce arcing) between the electrodes than does the plug firing with a negative polarity. As a result, in a wasted-spark configuration wherein current is successively induced in the secondary winding in the same direction, experience has particularly demonstrated that the center electrode of the always positive firing spark plug exhibits excessive and premature erosion and uneven wearing as compared to the always negative firing spark plug. That is, the useful life of the positive firing spark plug is significantly shorter than the useful life of the negative firing spark plug. Thus, the positive firing spark plug prematurely and undesirably threatens the overall functional integrity of the ignition system.
In an attempt to extend the useful life of the positive firing spark plug in a wasted-spark configuration, some engine manufacturers have specifically reduced the spark gap for only the positive firing spark plug, thereby reducing the firing voltage potential necessary for breaking down the spark gap in the positive firing plug. However, such a remedial attempt generally necessitates an increase in the complexity and cost of engine assembly, for the various cylinders in a given engine will then need to operate with various types of spark plugs with different spark gap settings.
Other engine manufacturers have done away with the traditional wasted-spark configuration and instead attempted to incorporate the two spark plugs for a given ignition coil within a unique diode-based type circuit, which is attached to the secondary winding of the ignition coil, so as to prevent positive firing of the spark plugs. Such diode-based circuits generally permit only one of the two spark plugs to fire during a given high tension pulse in the secondary winding, and the two spark plugs take turns negatively firing during consecutive high tension pulses. In this way, and in contrast to a wasted-spark configuration, the two spark plugs are prevented both from positively firing and from firing simultaneously during the same high tension current pulse in the secondary winding. As a result, the useful lives of both spark plugs are extended. See, for example, U.S. Pat. No. 5,425,348 issued to Bracken on Jun. 20, 1995. However, such a remedial attempt in addition to other non-traditional configurations generally necessitate an increase in the complexity and cost of certain aspects of an ignition system, for such configurations often require the utilization of numerous xe2x80x9csteeringxe2x80x9d or xe2x80x9cblockingxe2x80x9d diodes, one or more tapped primary windings, or multiple primary windings sharing the same secondary winding. See, for examples, U.S. Pat. No. 4,361,129 issued to Sugie et al on Nov. 30, 1982; U.S. Pat. No. 4,378,779 issued to Hachiga et al on Apr. 5, 1983; and U.S Pat. No. 4,463,744 issued to Tanaka et al on Aug. 7, 1984.
In light of the above, there is a present need in the art for a simple, flexible, and low-cost apparatus which will extend the useful lives of the spark plugs in an ignition system and also thereby extend the useful life of the overall ignition system.
The present invention is an ignition coil with control and driver apparatus having reverse polarity capability. The apparatus is suitable for a distributorless ignition system associated with an internal combustion engine. The apparatus responds to an ignition signal pulse train (ISPT) which is related to the compression and exhaust strokes of an internal combustion engine. According to the present invention, the apparatus basically includes, first of all, at least one ignition coil having a primary winding, a secondary winding, and a core. The primary winding and the secondary winding are wrapped about the core, and the primary winding has a first end and a second end. The apparatus also basically includes a pair of spark plugs for each ignition coil. The spark plugs are connected between opposite ends of the secondary winding and electrical ground. Lastly, the apparatus includes a circuit connected to the first end and the second end of the primary winding for directing electrical current through the primary winding in an opposite direction during each successive ignition signal pulse. In this way, the spark plugs simultaneously fire after each ignition signal pulse.
In a preferred embodiment of the apparatus according to the present invention, the circuit for directing electrical current through the primary winding includes both a driver circuit and a control circuit. The driver circuit is connected to the primary winding and serves to direct and drive electrical current through the primary winding. The control circuit is connected to the driver circuit and serves to control and activate the driver circuit. In addition, a capacitor is preferably connected between the first end and the second end of the primary winding of the ignition coil.
The driver circuit is compatible with a direct-current (DC) power supply and preferably includes both an activatable first sub-circuit and an activatable second sub-circuit. The activatable first sub-circuit is capable of electrically connecting the first end of the primary winding to the positive terminal of a direct-current power supply and also electrically connecting the second end of the primary winding to the negative terminal of the power supply. The activatable second sub-circuit is capable of electrically connecting the first end of the primary winding to the negative terminal of the same power supply and also electrically connecting the second end of the primary winding to the positive terminal of the power supply. In such an arrangement, the control circuit serves to altematingly activate the first sub-circuit and the second sub-circuit of the driver circuit in response to an ignition signal pulse train. In this way, the control circuit thereby directs electrical current through the primary winding of the ignition coil in an opposite direction during each successive ignition signal pulse. As a result, the spark plugs simultaneously fire after each ignition signal pulse.
In a highly preferred embodiment of the apparatus according to the present invention, the control circuit includes a J-K flip-flop, a first AND gate, and a second AND gate for controlling and activating the driver circuit. The J-K flip-flop preferably includes a reset input for receiving a pulse when the camshaft of an internal combustion engine reaches top dead center (TDC). In this way, ignition timing, spark timing, and overall synchronization between the apparatus according to the present invention and the stroke cycle of an internal combustion engine is properly maintained and ensured.
Advantages, design considerations, and applications of the present invention will become apparent to those skilled in the art when the detailed description of the best mode contemplated for practicing the invention, as set forth hereinbelow, is read in conjunction with the accompanying drawings.